Method for improving the magnetic properties of ferrous alloys



Jan. 31, 1939.

0. DAHL Er AL 2,145,712

METHOD FOR IMPROVING THE MAGNETIC PROPERTIES OF FERROUS ALLOYS INDUCTION Filed Feb. 15, 1936 Fig. I.

moucnow H Inventor's:

Otto D a h l,

Fhanz' Paw! b M 5 rhe r Attorne 2 Sheets-Sheet l I Jan. 31, 1939. Q DAHL ETAL ,145,712 METHOD FOR IMPROVING THE MAGNETIC PROPERTIES OF FERROUS ALLOYS Filed Feb. 15, 1936 2 Sheets-Sheet 2 Fig. 3.

INDUCTION Inventdrs: Otto Dahl,

Franz Pawle,

Patented Jail- 31, 1939 um'rso STATES PATENT OFFICE METHOD FOR IMPROVING THE MAGNETIC PROPERTIES OFFERROUS ALLOYS New York Application February 15, 1936, Serial No. 64,133

In G

I Claim.

In order to obtain a uniform rise of magnetization throughout a wide field-strength range, as well as a nearly complete saturation at low field strengths, it has been proposed to produce in magnetic materials, an ordered grain texture such as can be obtained by certain rolling and annealing processes. For instance, magnetic iron-nickel alloys can be cold-rolled,prior to thefinal annealing, with a reduction of thickness amounting to more than 90%, preferably more than 95%, after which the material is annealed at temperatures above the recrystallization limit. As a result of this treatment, an ordered position of the crystallites is obtained in the plates after the annealing, and

this ordered position has an extraordinary favorable influence on the magnetic properties.

The present invention is an improvement of these methods and consists in subjecting the alloys during cooling, after the final annealing, to the influence of a magnetic field, in such a way that, depending upon whether the magnetization curves, as a function of the field strength, are to have a steeper or flatter shape, the alloys are subjected either to the influence of a longitudinal or transverse magnetic field.

The terms, longitudinal and transverse, here,

imply respectively the direction of rolling or the direction at right angles to the direction of rolling. While the influence of a magnetic field applied during the cooling is known, it has been found unexpectedly, that by applying simultaneously the methods for obtaining an orderedgrain structure and the cooling under amagnetic field, the eiiect on magnetic properties could be considerably increased, and that said properties could be given a degree of perfection such as has not been obtained so far.

In the attached drawings, 'we have indicated graphically the results for three different alloy 40 combinations. The curves denoted by a represent in each case, the results obtained with specimens which, for the purpose of an ordered grain structure, have been subjected, prior to the final annealing, to a cold rolling resulting in a decrease in thickness exceeding 90%. On the other hand, the curvesdenoted by b"'represent the results obtained with specimens that had been subjected to a lesser amount of cold rolling such as had been resorted to formerly. The indexes l to 3 indicate whether the alloy specimens were subjected to a magnetic field during the cooling and, if so, to what magnetic field. Specimens with index I were cooled without the application of a magnetic field; the specimens with index 2 were cooled with the simultaneous application ermany March 11, 1935,

(Cl. 148-4) I of a longitudinal magnetic field, while specimens with index 3 were cooled with the simultaneous application of a transverse magnetic field.

Fig. 1 refers to a binary iron-nickel alloy with 40% nickel and iron; Fig. 2 refers to a binary terials; they were then reduced to a thickness of 0.3 mm, by way of forging or hot or cold rolling with intermediate annealing above the recrystallization temperature. The specimens of. group b were subjected, during the last cold rolling to a decrease in thickness amounting to that is, a decrease in thickness which is close to the limit of the conventional rolling process used in connection with such alloys. In contrast to this, the specimens of group a. were, in order to attain a good grain structure, subjected to a last cold rolling, which resulted in a decrease in thickness of 98.5%. Finally, all specimens were subjected to a last annealing at 1100 C. for two hours'in a hydrogen current.

The process, according to the invention, has diflerent-qualitative results, depending on the difierent alloys, However, it has been found that by using simultaneously a high degree of cold rolling (for obtaining an ordered'grain texture) and a longitudinal magnetic field during the cooling, there is always obtained a steeper magnetization curve which extends linearly through a wider induction range. On the other hand, the simultaneous application of a high degree of cold rolling and ot atransverse magnetic field during cooling, results always in a magnetizing curve. which is rectilinear through an unusually wide.

field-strength range, In particular, the magnetization characteristic of the alloy represented in Fig.- 2, which consists of equal parts of iron and nickel, is steeper than that of the magnetization curve of the alloy according to Fig. 1, which alloy has 40% of nickel and 60% of iron. Thus, if iorcertain reasons, a linear magnetization characteristicis desired through a field-strength range which is as wide as possible, the alloy, according to Fig. 1, should be given preference to the alloy according to Fig. 2. This condition will always obtain whenever the field strength cannot be reduced at will by the selection of a small number of turns in a coil, However, if this reduction is possible, so that when dimensioning a coil, only the induction need be considered, the alloy, according to Fig. 2, should be given preference over the alloy of Fig. 1, for with the alloy, according to Fig. 2, the same efiect can be obtained with a smaller amount of material.

Fig. 3 shows that the application of the method, according to the invention, is not limited to binary iron-nickel alloys, but that it can be also successfully applied to the iron-nickel-cobalt alloys. The improvement of the steep rise of the characteristic by the simultaneous application of a high degree of cold rolling and a longitudinal magnetic field during the cooling is, here, not so marked as was the case with. the application of the longitudinal magnetic field in connection with the binary iron-nickel alloys, for the application of a magnetic field alone, permits obtaining a very steep curve. On the other hand, the improvement of the linear rise through a wide field-strength range, by applying simultaneously a high degree of stretching and a transversal magnetic field, is here quite considerable Fig. 3 shows that the uniform rise begins practically at the point of origin and that it continues until saturation sets in. The hysteresis loop returns with the low remanence of a thousand gauss, nearly as linearly as it rises. Such an alloy is of major importance for communication engineering, for instance for Krarup lines, and also for transmitters, for a magnetic body consisting of that particular alloy, operates practically without harmonics.. For this reason, an alloy of that composition and treatment must be primarily applied in all those cases which deal with circuits in which the harmonics have a disturbing eifect, even at a slight amplitude. Such fields of application exist always in those cases when several signals are to be transmitted through one'and the same line by means of different carrier frequencies, for in these cases, the harmonics of one channel come within the transmitting range of the other channel and may thus entail a mutual interference of both channels.

The application of the object of the invention is not limited to the alloys which have been chosen by way of example. The entirely different composition of the alloys in Figs. 1 and 2 on the one hand, and in Fig. 3 on the other hand, indicates plainly that the method according to the invention will permit a considerable influencing of the magnetic properties in nearly all ferromagnetic substances. Which one of the known alloys must be chosen for any particular purpose, can be determined from case to case by a simple test. The method is particularly advantageous in connection with all those alloys in which the application of the conventional annealing treatments alone, that is to say, primarily, the

application of a slower cooling will result in a rectilinear magnetization characteristic through a certain field strength range. These alloys are, 'on the one hand, the binary iron-nickel alloys with or without the addition of small quantities of third substances (up to about 10%) and, on the other hand, the iron-nickel-cobalt alloys such as they have been described by Elmen.

What we claim as new and desire to secure by Letters Patent of the United States, is:

A method for improving the magnetic properties of alloys consisting of nickel and iron which comprises cold working the alloy to eifect a reduction in thickness of more than 90%, an-

nealing the alloy and during cooling subjecting it to the influence of a longitudinal magnetic field.

O'I'IO DAHL. FRANZ PAW'LEK. 

